Aggregate material, such as sand, gravel or top-soil, is often loaded at a first location, trucked from the first location to a second location, and unloaded at the second location.
In known devices, an aggregate carrying body is mounted on a truck. The body has sloping sides that lead to an opening at the bottom of the body. A first conveyor below the opening carries aggregate that falls through the opening to an unloading device, such as a second conveyor running at high speed.
In known devices, slidable gates are mounted between the opening at the bottom of the body and the first conveyor. The gates are moved from an open position to a closed position by means such as a hydraulic ram mounted between the gate and the body. In closed position, the gate covers the opening and the aggregate cannot fall from the body to the first conveyor for unloading. In open position, the opening is not covered, and the aggregate can fall or flow from the body through the opening to the first conveyor below.
In a known unloading device, a series of four gates are positioned along the length of the opening. These gates can be opened or closed individually to help control the rate of flow of aggregate material from the body through the opening and onto the first conveyor. For example, if a higher rate of flow is desired, all four gates will be opened. If a slower rate of flow is desired, one or more of the gates will be closed. When the truck is moved from a first to a second location, all gates are closed.
These known systems have a number of disadvantages. First, aggregate material that clumps, such as top-soil, may not flow easily through the opening. Second, the mechanism for opening and closing the gates is moderately complex, thus increasing both the initial cost of the unloading device and the cost of ongoing maintenance and repair. Finally, positioning the gates between the aggregate carrying body and the first conveyor requires that the aggregate carrying body be raised and mounted higher off the ground than if there were no gates. Mounting the body higher off the ground results in a higher center of gravity (and hence instability of the loaded truck) or reduces the carrying capacity of the aggregate carrying body.